Heat sink material and method of manufacturing the heat sink material

ABSTRACT

Graphite is placed in a case, and the case is set in a furnace. The interior of the furnace is subjected to sintering to produce a porous sintered member of graphite. After that, the case with the porous sintered member therein is taken out of the furnace, and is set in a recess of a press machine. Subsequently, molten metal of metal is poured into the case, and then a punch is inserted into the recess to forcibly press the molten metal in the case downwardly. Open pores of the porous sintered member are infiltrated with the molten metal of the metal by the pressing treatment with the punch.

TECHNICAL FIELD

The present invention relates to a heat sink material for construction aheat sink which efficiently releases heat generated, for example, froman IC chip, and a method of producing the same.

BACKGROUND ART

In general, heat is an enemy for the IC chip and it is necessary thatthe internal temperature thereof does not exceed the maximum allowablejunction temperature. The electric power consumption per operation areais large in the semiconductor device such as a power transistor or asemiconductor rectifier element. Therefore, the generated heat amountcannot be sufficiently released with only the heat amount released froma case (package) and a lead of the semiconductor device. It is fearedthat the internal temperature of the device may be raised to causethermal destruction.

This phenomenon also occurs in the same manner in the IC chip whichcarries a CPU. The amount of heat generation is increased during theoperation in proportion to the improvement in clock frequency. It is animportant matter to make the thermal design in consideration of the heatrelease.

In the thermal design for preventing the thermal destruction or thelike, element design or package design is made on condition that a heatsink having a large heat release area is secured to a case (package) ofthe IC chip.

In general, a metal material such as copper and aluminum, which has agood thermal conductivity, is used as a material for the heat sink.

Recently, the IC chip such as CPU and memory is in a trend that the ICchip itself has a large size in accordance 10, with the high degree ofintegration of the element and the enlargement of the element-formingarea, while it is intended to drive the IC chip at low electric powerfor the purpose of low electric power consumption. When the IC chip hassuch a large size, it is feared that the stress caused by the differencein thermal expansion between the semiconductor substrate (siliconsubstrate or GaAs substrate) and the heat sink is increased, and thatthe peeling-off phenomenon and the mechanical destruction occur in theIC chip.

In order to avoid such an inconvenience, for example, it may be pointedout that the low electric power driving of the IC chip should berealized, and the heat sink material should be improved. The lowelectric power driving of the IC chip is realized in the level of notmore than 3.3 V at present and the TTL level (5 V) which has beenhitherto used as the power source voltage becomes obsolete.

As for the constitutive material for the heat sink, it is insufficientto consider only the thermal conductivity. It is necessary to select amaterial which has a coefficient of thermal expansion approximatelyidentical with those of silicon and GaAs, which are used as thesemiconductor substrate, while having a high thermal conductivity at thesame time.

A variety of reports have been made in relation to the improvement ofthe heat sink material, including, for example, a case in which aluminumnitride (AlN) is used and a case Cu (copper)-W (tungsten) is used. AlNis excellent in balance between the thermal conductivity and the thermalexpansion. Especially, the coefficient of thermal expansion of AlN isapproximately coincident with the coefficient of thermal expansion ofSi. Therefore, AlN is preferred as a heat sink material for asemiconductor device in which a silicon substrate is used as thesemiconductor substrate.

Cu—W is a composite material having both of the low thermal expansion ofW and the high thermal conductivity of Cu. Further, Cu—W is mechanicallymachined with ease. Therefore, Cu—W is preferred as a constitutivematerial for a heat sink having a complicated shape.

Other instances have been suggested, wherein metal Cu is contained in aratio of 20 to 40% by volume in a ceramic base material containing amajor component of SiC (conventional technique 1, see Japanese Laid-OpenPatent Publication No. 8-279569), and wherein a powder-sintered porousmember of an inorganic substance is infiltrated with Cu by 5 to 30% byweight (conventional technique 2, see Japanese Laid-Open PatentPublication No. 59-228742).

The heat sink material concerning the conventional technique 1 isproduced in the powder formation in which a green compact of SiC andmetal Cu is formed to produce a heat sink. Therefore, the coefficient ofthermal expansion and the coefficient of thermal conductivity representonly theoretical values. It is impossible to obtain the balance betweenthe coefficient of thermal expansion and the coefficient of thermalconductivity required for actual electronic parts etc.

The conventional technique 2 uses a low ratio of Cu with which thepowder-sintered porous member composed of the inorganic substance isinfiltrated. It is feared that a limit may arise to enhance the thermalconductivity thereby.

On the other hand, a composite material, which is obtained by combiningcarbon and metal, has been developed and practically used. However, sucha composite material is used, for example, as an electrode for thedischarge machining when the metal is Cu. When the metal is Pb, such acomposite material is used, for example, as a bearing material. No caseis known for the application as a heat sink material.

That is, in the present circumstances, the coefficient of thermalconductivity is at most 140 W/mK for the composite material obtained bycombining carbon and metal, which cannot satisfy the value of not lessthan 160 W/mK required for the heat sink material for the IC chip.

DISCLOSURE OF THE INVENTION

The present invention has been made taking the foregoing problems intoconsideration, and an object thereof is to provide a heat sink materialwhich makes it possible to obtain characteristics adapted to the balancebetween the coefficient of thermal expansion and the coefficient ofthermal conductivity required for actual electronic parts (includingsemiconductor devices) etc.

Another object of the present invention is to provide a method ofproducing with ease a heat sink material having characteristics adaptedto the balance between the coefficient of thermal expansion and thecoefficient of thermal conductivity required for actual electronic parts(including semiconductor devices) etc., and the method for improving theproductivity of a high quality heat sink.

According to the present invention, there is provided a heat sinkmaterial comprising carbon or allotrope thereof and metal. An averagecoefficient of thermal conductivity of those in directions of orthogonalthree axes, or a coefficient of thermal conductivity in a direction ofany axis is not less than 160 W/mK. Accordingly, it is possible toobtain the heat sink material in which the coefficient of thermalexpansion is approximately coincident with those of the ceramicsubstrate (such as silicon or GaAs), and the semiconductor substrate(such as silicon or GaAs), etc., and the thermal conductivity issatisfactory.

It is also possible to obtain the heat sink material wherein the averagecoefficient of thermal conductivity of those in the directions of theorthogonal three axes, or the coefficient of thermal conductivity in thedirection of any axis is not less than 180 W/mK, and wherein acoefficient of thermal expansion is 1×10⁻⁶ to 10×10⁻⁶/° C.

It is preferable that the allotrope is graphite or diamond. Further, itis preferable that the carbon or the allotrope thereof has a coefficientof thermal conductivity of not less than 100 W/mK.

The heat sink material can be constructed by infiltrating a poroussintered member with the metal, the porous sintered member beingobtained by sintering the carbon or the allotrope thereof to form anetwork.

In this case, it is preferable that a porosity of the porous sinteredmember is 10 to 50% by volume, and an average pore diameter is 0.1 to200 μm. It is preferable that as for volume ratios between the carbon orthe allotrope thereof and the metal, the volume ratio of the carbon orthe allotrope thereof is within a range from 50 to 80% by volume, andthe volume ratio of the metal is within a range from 50 to 20% byvolume.

It is preferable that an additive is added to the carbon or theallotrope thereof for decreasing a closed porosity when the carbon orthe allotrope thereof is sintered. The additive may be exemplified bySiC and/or Si.

It is also preferable that the heat sink material is constructed byinfiltrating a preformed product with the metal, the preformed productbeing prepared by mixing water or a binder with powder of the carbon orthe allotrope thereof, and forming an obtained mixture under apredetermined pressure. In this case, it is preferable that an averagepowder particle size of the powder is 1 to 2000 μm, and a length ratiois not more than 1:5 between a direction in which the powder has aminimum length and a direction in which the powder has a maximum length.In this case, although there is no strong network, it is possible tomake an arbitrary shape.

It is preferable that as for volume ratios between the carbon or theallotrope thereof and the metal, the volume ratio of the carbon or theallotrope thereof is within a range from 20 to 80% by volume, and thevolume ratio of the metal is within a range from 80 to 20% by volume.

It is also preferable that the heat sink material is constructed bymixing powder of the carbon or the allotrope thereof with the metaldissolved into a liquid state or a solid-liquid co-existing state toobtain a mixture, and casting the obtained mixture.

It is preferable that a closed porosity of the produced heat sinkmaterial is not more than 12% by volume.

It is preferable that an element for improving wettability at aninterface is added to the metal. It is possible to adopt one or more ofthose selected from Te, Bi, Pb, Sn, Se, Li, Sb, Tl, Ca, Cd, and Ni asthe element to be added. Especially, Ni has an effect that carbon iseasily dissolved and easily infiltrated.

It is preferable that the metal is added with an element for improvingreactivity with the carbon or the allotrope thereof. It is possible toadopt one or more of those selected from Nb, Cr, Zr, Be, Ti, Ta, V, B,and Mn, as the element to be added.

It is preferable that an element, which has a temperature range of solidphase/liquid phase of not less than 30° C., desirably not less than 50°C., is added to the metal in order to improve molten metal flowperformance. Accordingly, it is possible to reduce the dispersion duringthe infiltration, the residual pores are decreased, and it is possibleto improve the strength. The equivalent effect can be also obtained byincreasing the infiltration pressure. It is possible to adopt one ormore of those selected from Sn, P, Si, and Mg as the element to beadded. Further, it is preferable that an element for lowering a meltingpoint is added to the metal. The element to be added is Zn, for example.

It is preferable that an element for improving the coefficient ofthermal conductivity is added to the metal. In this case, it ispreferable that an element for improving the coefficient of thermalconductivity is added to the metal, and an alloy of the element and themetal is obtained by segregation or the like after a heat treatment,processing, and reaction with carbon, the alloy has a coefficient ofthermal conductivity of not less than 10 W/mK. It is preferable that thecoefficient of thermal conductivity is desirably not less than 20 W/mK,more desirably not less than 40 W/mK, and most desirably not less than60 W/mK.

It is the known effect brought about by the heat treatment that thecoefficient of thermal conductivity is improved by combining aging ofthe added element, annealing, and processing. The feature describedabove is based on the use of this effect. It is also known that thereaction with carbon decreases the added element of copper, aluminum,and silver, resulting in improvement in coefficient of thermalconductivity. Further, it is also known that the added element isdeposited on the surface etc. owing to the segregation or the like whenthe infiltrated metal is solidified, and the coefficient of thermalconductivity as a whole is improved. Therefore, it is possible toutilize such an effect as well.

The heat sink material can be also constructed such that powder of thecarbon or the allotrope thereof is mixed with powder of the metal toobtain a mixture, and the obtained mixture is formed under apredetermined pressure. In this case, it is preferable that an averagepowder particle size of the powder of the carbon or the allotropethereof and the powder of the metal is 1 to 500 μm.

The heat sink material can be also constructed such that a pulverizedcut material of the carbon or the allotrope thereof is mixed with powderof the metal to obtain a mixture, and the obtained mixture is formed ata predetermined temperature under a predetermined pressure.

When the heat sink material is constructed by the forming process asdescribed above, it is preferable that as for volume ratios between thecarbon or the allotrope thereof and the metal, the volume ratio of thecarbon or the allotrope thereof is within a range from 20 to 60% byvolume, and the volume ratio of the metal is within a range from 80 to40% by volume. Accordingly, it is possible to obtain the heat sinkmaterial in which the coefficient of thermal conductivity is not lessthan 200 W/mK, and a coefficient of thermal expansion is 3×10⁻⁶ to14×10⁻⁶/° C.

It In this case, it is preferable that an additive making it possible toperform re-sintering after forming process is added to the carbon or theallotrope thereof. The additive may be exemplified by SiC and/or Si.

It is preferable that a low melting point metal for improvingwettability at an interface is added to the metal. It is possible toadopt one or more of those selected from Te, Bi, Pb, Sn, Se, Li, Sb, Se,Tl, Ca, Cd, and Ni as the low melting point metal.

It is preferable that an element for improving reactivity with thecarbon or the allotrope thereof is added to the metal. It is possible toadopt one or more of those selected from Nb, Cr, Zr, Be, Ti, Ta, V, B,and Mn as the element to be added.

It is preferable that an element, which has a temperature range of solidphase/liquid phase of not less than 30° C., desirably not less than 50°C., is added to the metal in order to improve molten metal flowperformance. Accordingly, it is possible to reduce the dispersion duringthe infiltration, the residual pores are decreased, and it is possibleto improve the strength. The same or equivalent effect can be alsoobtained by increasing the infiltration pressure. It is possible toadopt one or more of those selected from Sn, P, Si, and Mg as theelement to be added. Further, it is preferable that an element fordecreasing a melting point is added to the metal. The element to be inadded is Zn, for example.

It is also preferable that a carbide layer is formed on a surface of thecarbon or the allotrope thereof by means of a reaction at least betweenthe carbon or the allotrope thereof and the element to be added. In thiscase, it is possible to adopt one or more of those selected from Ti, W,Mo, Nb, Cr, Zr, Be, Ta, V, B, and Mn as the element to be added.

It is possible to adopt at least one selected from Cu, Al, and Ag, asthe metal to be combined with the carbon or the allotrope thereof. Eachof the metals Cu, Al, and Ag has high conductivity.

In the present invention, a ratio of coefficient of thermal conductivityis not more than 1:5 between a direction in which the coefficient ofthermal conductivity is minimum and a direction in which the coefficientof thermal conductivity is maximum. Accordingly, the coefficient ofthermal conductivity has a characteristic approximately equal to theisotropic characteristic. Therefore, the heat is diffused in awell-suited manner. Thus, the heat sink material is preferably used fora heat sink. Further, it is unnecessary to consider the direction ofinstallation case by case, thereby advantageous on the practicalmounting.

According to another aspect of the present invention, there is provideda method of producing a heat sink material, comprising the steps of:sintering carbon or in allotrope thereof to form a network for obtaininga porous sintered member; infiltrating the porous sintered member withmetal; and cooling the porous sintered member infiltrated with at leastthe metal.

Accordingly, it is possible to easily produce the heat sink materialhaving a coefficient of thermal expansion approximately coincident withthose of a ceramic substrate (such as silicon or GaAs), a semiconductorsubstrate (such as silicon or GaAs), etc., and having good thermalconductivity. It is possible to improve the productivity of a heat sinkhaving a high quality.

It is also preferable that in the sintering step, the carbon or theallotrope thereof is placed in a vessel, and an interior of the vesselis heated to produce the porous sintered member of the carbon or theallotrope thereof.

It is also preferable that in the infiltrating step, the porous sinteredmember is immersed in molten metal of the metal introduced into avessel, and the porous sintered member is infiltrated with the moltenmetal by introducing infiltrating gas into the vessel to pressurize aninterior of the vessel. In this case, it is preferable that the force ofthe pressurization is four to five times as strong as a compressivestrength of the porous sintered member of the carbon or the allotropethereof or less than four to five times the compressive strength of theporous sintered member. Alternatively, the force of the pressurizationis preferably 1.01 to 202 MPa (10 to 2000 atmospheres). In the coolingstep in this case, the infiltrating gas in a vessel may be vented, andcooling gas may be quickly introduced to cool an interior of the vessel.

The following method is exemplified as another production method. Thesintering step includes a step of setting the carbon or the allotropethereof in a case, and a step of preheating an interior of the case toprepare the porous sintered member of the carbon or the allotropethereof. The infiltrating step includes a step of setting the case in amold of a press machine, a step of pouring molten metal of the metalinto the case, and a step of forcibly pressing the molten metaldownwardly with a punch of the press machine to infiltrate the poroussintered member in the case with the molten metal.

In this case, it is preferable that a pressure of the forcible pressingby the punch is four to five times as strong as a compressive strengthof the porous sintered member of the carbon or the allotrope thereof orless than four to five times the compressive strength of the poroussintered member. Alternatively, the preferable pressure is 1.01 to 202MPa (10 to 2000 atmospheres). It is preferable that a mold formed with agas vent hole for venting any remaining gas in the porous sinteredmember or formed with a gap for venting gas.

It is also preferable that in the cooling step, the heat sink material,in which the porous sintered member is infiltrated with the metal, iscooled by cooling gas blown thereagainst or by using a cooling zone or acooling mold where cooling water is supplied.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing water or a binder with powder of carbon or allotropethereof to obtain a mixture; forming the obtained mixture into apreformed product under a predetermined pressure; and infiltrating thepreformed product with metal.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing powder of carbon or allotrope thereof with metaldissolved into a liquid state or a solid-liquid co-existing state toobtain a mixture; and casting the obtained mixture.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing powder of carbon or allotrope thereof with powder ofmetal to obtain a mixture; and pressurizing the obtained mixture placedin a mold of a hot press machine at a predetermined temperature under apredetermined pressure to form into the heat sink material.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing powder of carbon or allotrope thereof with powder ofmetal to obtain a mixture; preforming the obtained mixture to prepare apreformed product; and pressurizing the preformed product placed in amold of a hot press machine at a predetermined temperature under apredetermined pressure to form into the heat sink material.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing a pulverized cut material of carbon or allotropethereof with powder of metal, and preforming to prepare a mixture; andpressurizing the mixture placed in a mold of a hot press machine at apredetermined temperature under a predetermined pressure to form intothe heat sink material.

According to still another aspect of the present invention, there isprovided a method of producing a heat sink material, comprising thesteps of: mixing a pulverized cut material of carbon or allotropethereof with powder of metal to obtain a mixture; preforming theobtained mixture to prepare a preformed product; and pressurizing thepreformed product placed in a mold of a hot press machine at apredetermined temperature under a predetermined pressure to form intothe heat sink material.

In the production methods described above, it is preferable that thepredetermined temperature is relatively −10° C. to −50° C. with respectto a melting point of the metal, and it is preferable that thepredetermined pressure is 10.13 to 101.32 MPa (100 to 1000 atmospheres).

In the production methods described above, it is also preferable thatthe heat sink material is heated to a temperature of not less than amelting point of the metal after the pressurizing step.

Further, it is also preferable that the metal is at least one selectedfrom Cu, Al, and Ag.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view illustrating construction of a heat sinkmaterial according to a first embodiment;

FIG. 2A shows, with partial cutaway, a front of a high pressure vesselto be used in a first production method;

FIG. 2B shows, with partial cutaway, a side of the high pressure vessel;

FIG. 3 shows a block diagram illustrating steps of the first productionmethod;

FIG. 4 shows a block diagram illustrating steps of a first modifiedmethod of the first production method;

FIG. 5 shows a block diagram illustrating steps of a second modifiedmethod of the first production method;

FIG. 6 shows an arrangement of a furnace to be used in a secondproduction method;

FIG. 7 shows a press machine to be used in the second production method;

FIG. 8 shows a block diagram illustrating steps of the second productionmethod;

FIG. 9 shows a perspective view illustrating construction of a heat sinkmaterial according to a second embodiment;

FIG. 10 shows an arrangement of a preforming machine to be used in athird production method;

FIG. 11 shows an arrangement of a hot press machine to be used in thethird production method;

FIG. 12 shows a block diagram illustrating steps of the third productionmethod;

FIG. 13 shows a block diagram illustrating steps of a fourth productionmethod;

FIG. 14 shows an arrangement of a hot press machine to be used in thefourth production method;

FIG. 15 shows a perspective view illustrating construction of a heatsink material according to a third embodiment;

FIG. 16 shows a block diagram illustrating steps of a fifth productionmethod;

FIG. 17 shows a table illustrating characteristics of the heat sinkmaterial according to the fifth production method;

FIG. 18 shows a block diagram illustrating steps of a sixth productionmethod;

FIG. 19 shows a table illustrating results of an exemplary experimentconcerning a carbon P;

FIG. 20 shows a table illustrating results of an exemplary experimentconcerning a carbon M;

FIG. 21 shows a table illustrating results of an exemplary experimentconcerning a carbon N;

FIG. 22 shows a table illustrating characteristics of carbons P, M, andN;

FIG. 23 shows a table in which representative examples concerning a casebased on a mold press and a case based on gas pressurization areextracted from the experimental results;

FIG. 24 shows characteristic curves illustrating the change of theporosity and the density with respect to the infiltration pressure;

FIG. 25 shows characteristic curves illustrating the relationshipbetween the measured density and the average density for respectivelots;

FIG. 26 shows a characteristic curve illustrating the change of thecoefficient of thermal conductivity with respect to the infiltrationpressure;

FIG. 27 shows a characteristic curve illustrating the change of thecompressive strength with respect to the infiltration pressure;

FIG. 28 shows a characteristic curve illustrating the change of thedensity with respect to the infiltration pressure;

FIG. 29 shows a characteristic curve illustrating the change of thecoefficient of thermal expansion with respect to the infiltrationpressure;

FIG. 30 shows a table illustrating the difference of the reactionsituation of SiC/Cu and the infiltration situation of Cu whenappropriate change is made for the porosity of SiC, the pore diameter,the presence or absence of Ni plating, the presence or absence of Siinfiltration, the infiltration temperature, the pressurization, thepressurization time, and the cooling speed;

FIG. 31 shows characteristic curves illustrating the change of theresidual pore with respect to the infiltration pressure;

FIG. 32 shows characteristic curves illustrating the change of theresidual pore with respect to the additive element;

FIG. 33 shows a schematic arrangement of a hot press machine to be usedin a seventh production method;

FIG. 34 shows a block diagram illustrating steps of the seventhproduction method;

FIG. 35A shows a plan view illustrating a packing member;

FIG. 35B shows a sectional view taken along a line XXIVB—XXIVB shown inFIG. 35A;

FIG. 36 shows a schematic arrangement of another exemplary hot pressmachine to be used in the seventh production method;

FIG. 37 shows a schematic arrangement of a hot press machine to be usedin a modified method of the seventh production method;

FIG. 38 shows a block diagram illustrating steps of the modified methodof the seventh production method;

FIG. 39 shows a schematic arrangement of a hot press machine to be usedin an eighth production method; and

FIG. 40 shows a block diagram illustrating steps of the eighthproduction method.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the heat sink material and the method ofproducing the same according to the present invention will be explainedbelow with reference to FIGS. 1 to 40.

As shown in FIG. 1, a heat sink material 10A according to the firstembodiment comprises a porous sintered member 12 obtained by sinteringcarbon or allotrope thereof to form a network, in which the poroussintered member 12 is infiltrated with metal 14.

In this case, the carbon preferably used or the allotrope thereof has acoefficient of thermal conductivity of not less than 100 W/mK, desirablynot less than 150 W/mK (estimated value in a state in which no poreexists), and more desirably not less than 200 W/mK (estimated value in astate in which no pore exists).

This embodiment is illustrative of a case of the heat sink material inwhich open pores of the porous sintered member 12 of graphite having acoefficient of thermal conductivity of not less than 100 W/mK areinfiltrated with copper. Those usable as the metal 14 of infiltrationother than copper include aluminum and silver.

As for the volume ratios of the porous sintered member 12 and the metal14, the volume ratio of the porous sintered member 12 is within a rangefrom 50 to 80% by volume, and the volume ratio of the metal 14 is withina range from 50 to 20% by volume. Accordingly, it is possible to obtainthe heat sink material in which the average coefficient of thermalconductivity of those in the directions of the orthogonal three axes, orthe coefficient of thermal conductivity in the direction of any axis is180 to 220 W/mK or more, and in which the coefficient of thermalexpansion is 1×10⁻⁶ to 10×10⁻⁶/° C.

The porosity of the porous sintered member 12 is desirably 10 to 50% byvolume, for the following reason. That is, if the porosity is not morethan 10% by volume, it is impossible to obtain the average coefficientof thermal conductivity of those in the directions of the orthogonalthree axes, or the coefficient of thermal conductivity in the directionof any axis of not less than 180 W/mK (room temperature). If theporosity exceeds 50% by volume, then the strength of the porous sinteredmember 12 is lowered, and it is impossible to suppress the coefficientof thermal expansion to be not more than 15.0×10⁻⁶/° C.

It is desirable that the value of the average open pore diameter (porediameter) of the porous sintered member 12 is 0.1 to 200 μm. If the porediameter is less than 0.1 μm, then it is difficult to infiltrate theinterior of the open pores with the metal 14, and the coefficient ofthermal conductivity is lowered. On the other hand, if the pore diameterexceeds 200 μm, then the strength of the porous sintered member 12 islowered, and it is impossible to suppress the coefficient of thermalexpansion to be low.

As for the distribution (pore distribution) in relation to the averageopen pores of the porous sintered member 12, it is preferable that notless than 90% by volume of the pores having diameters from 0.5 to 50 μmare distributed. If the pores of 0.5 to 50 μm are distributed by lessthan 90% by volume, then the open pores, which are not infiltrated withthe metal 14, are increased, and the coefficient of thermal conductivitymay be lowered.

As for the closed porosity of the heat sink material 10A obtained byinfiltrating the porous sintered member 12 with the metal 14, it ispreferable that the closed porosity is not more than 12% by volume. Ifthe closed porosity exceeds 5% by volume, the coefficient of thermalconductivity may be lowered.

An automated porosimeter (trade name: Autopore 9200), which is producedby Shimadzu Corporation, was used to measure the porosity, the porediameter, and the pore distribution.

In the heat sink material 10A according to the first embodiment, it ispreferable that the graphite is added with an additive which reduces theclosed porosity when the graphite is sintered. The additive isexemplified by SiC and/or Si. Accordingly, it is possible to decreasethe closed pores upon the sintering, and it is possible to improve theinfiltration ratio of the metal 14 with respect to the porous sinteredmember 12.

It is also preferable that an element, which reacts with the graphite,may be added to the graphite. The element to be added is exemplified byone or more of those selected from Ti, W, Mo, Nb, Cr, Zr, Be, Ta, V, B,and Mn. Accordingly, a reaction layer (carbide layer) is formed on thesurface of the graphite (including the surface of the open pore) duringthe sintering of the graphite. The wettability is improved with respectto the metal 14 with which the open pores of the graphite areinfiltrated. The infiltration can be performed at a low pressure.Further, fine open pores can be also infiltrated with the metal.

On the other hand, it is preferable that one or more of those selectedfrom Te, Bi, Pb, Sn, Se, Li, Sb, Tl, Ca, Cd, and Ni are added to themetal 14 with which the porous sintered member 12 is infiltrated.Accordingly, the wettability is improved for the interface between theporous sintered member 12 and the metal 14. The metal 14 easily entersthe open pores of the porous sintered member 12. Especially, Ni makescarbon easily dissolved and subject to the infiltration.

It is preferable that one or more of those selected from Nb, Cr, Zr, Be,Ti, Ta, V, B, and Mn are added to the metal 14 with which the poroussintered member 12 is infiltrated. Accordingly, the reactivity betweenthe graphite and the metal is improved. The graphite and the metaleasily make tight contact with each other in the open pores. It ispossible to suppress the occurrence of closed pores.

Further, it is preferable that an element having a temperature range ofsolid-liquid phase of not less than 30° C., desirably not less than 50°C., for example, one or more of those selected from Sn, P, Si, and Mgare added to the metal 14 with which the porous sintered member 12 isinfiltrated. That is because the molten metal flow performance isimproved and the residual pores are decreased. Accordingly, it ispossible to reduce the dispersion upon the infiltration. Further, theresidual pores are decreased, and it is possible to improve thestrength. The equivalent effect can be also obtained by increasing theinfiltration pressure. It is preferable that an element to lower themelting point is added to the metal 14. Zn can be an additive element,for example.

Next, explanation will be made with reference to FIGS. 2A to 8 forseveral methods of producing the heat sink material 10A according to thefirst embodiment.

Both of first and second production methods of producing the heat sinkmaterial 10A according to the first embodiment comprise a sintering stepof producing the porous sintered member 12 by sintering graphite to forma network, and an infiltrating step of infiltrating the porous sinteredmember 12 with the metal 14.

As specifically shown in FIGS. 2A and 2B by way of example, the firstproduction method is carried out by using a high pressure vessel 30. Thehigh pressure vessel 30 is provided with rotary shafts 38 atapproximately central portions of both side plates 34, 36 of a boxycasing 32, respectively. The casing 32 itself is rotatable about thecenter of the rotary shafts 38.

A refractory vessel 40 and a heater 42 for heating the refractory vessel40 are provided in the casing 32. The refractory vessel 40 is abox-shaped object provided with a hollow section 44. An opening 46communicating with the hollow section 44 is provided at a centralportion in the height direction at one side surface. An ingot of themetal 14 or molten metal of the metal 14 as a material for theinfiltration is set in one part of the hollow section (hereinafterreferred to as a “first chamber 44 a”) of the hollow section 44 which isdivided by the center of the opening 46.

A plurality of the porous sintered members 12 as a material subjected tothe infiltration are attached to the other part of the hollow section(hereinafter referred to as a “second chamber 44 b”). A supportmechanism for the porous sintered members 12 is provided so that theporous sintered members 12 do not fall downwardly even when the secondchamber 44 b is located upwardly. The heater 42 has a structure which isnot destroyed even at a high pressure of 300 MPa.

The high pressure vessel 30 is provided with a suction tube 48 forevacuation, and an introducing tube 50 and a discharge tube 52 for a gasapplying high pressure and a cooling gas.

Next, explanation will be made with reference to FIG. 3 for the firstproduction method based on the use of the high pressure vessel 30.

At first, in step S1, the porous sintered member 12 of graphite isprepared by performing a step of forming graphite into a rod shape, astep of infiltrating graphite with a pitch (a kind of coal tar), and astep of heating and sintering graphite.

When the graphite is formed to be the rod shape, the pitch is mixed withgraphite powder and extruded in an atmosphere at about 150° C. into therod shape (φ100 to φ600, the length is about 3000 mm). The graphite atthis stage includes many pores, and it has a low coefficient of thermalconductivity.

Subsequently, vacuum degassing is performed in order to decrease thepores of the graphite. The graphite is infiltrated with the pitch in thevacuum and sintered at about 1000° C. These steps are repeated aboutthree times.

Then, the graphite is further heated and sintered in a furnace at about3000° C. in order to improve the coefficient of thermal conductivity. Inthis procedure, the furnace is covered with carbon powder in order toprevent the graphite from burning, and the graphite itself is coveredwith carbon powder. The step of heating the graphite may be performed bydirectly applying electricity to the graphite to effect heating andsintering.

In accordance with the above procedure, the porous sintered member 12 isobtained. It is desirable that the porous sintered member 12 is furtherpre-machined depending on the shape of the final product.

After that, in step S2, for the initial state the high pressure vessel30 is located such that the first chamber 44 a is positioned at thelower side of the refractory vessel 40 provided inside of the highpressure vessel 30.

After that, the porous sintered members 12 and the ingot of the metal 14are placed in the refractory vessel 40 of the high pressure vessel 30.The ingot of the metal 14 is arranged in the first chamber 44 a of therefractory vessel 40, and the porous sintered members 12 are set in thesecond chamber 44 b (step S3). At this time, it is preferable that theporous sintered members 12 are preheated beforehand. The preheating isperformed such that the porous sintered member 12 is set in a carboncase or it is covered with a heat-insulating material. When thetemperature becomes a predetermined temperature, the porous sinteredmember 12 is set to the second chamber 44 b as described above exactlyin the state in which the porous sintered member 12 is set in the caseor it is covered with the heat-insulating material.

Next, the high pressure vessel 30 (and the refractory vessel 40) istightly enclosed, and then the interior of the high pressure vessel 30is evacuated by the aid of the suction tube 48 to give a negativepressure state in the high pressure vessel 30 (step S4).

The electric power is applied to the heater 42 to heat and melt themetal 14 in the first chamber 44 a (step S5). In the followingdescription, the heated and melted metal 14 is referred to as “moltenmetal 14” as well for convenience.

After that, when the molten metal 14 in the first chamber 44 a arrivesat a predetermined temperature, the high pressure vessel 30 is rotatedby 180 degrees (step S6). As a result of the rotating operation, thefirst chamber 44 a is located at the upper side. Therefore, the moltenmetal 14 in the first chamber 44 a falls by its own weight into thesecond chamber 44 b which is disposed at the lower side. Then, theporous sintered members 12 are immersed in the molten metal 14.

Subsequently, an infiltrating gas is introduced into the high pressurevessel 30 via the gas-introducing tube 50 to pressurize the interior ofthe high pressure vessel 30 (step S7). Owing to this pressurizationtreatment, the open pores of the porous sintered members 12 areinfiltrated with the molten metal 14.

The procedure immediately proceeds to the cooling step at the point oftime when the infiltrating step is completed. In the cooling step, thehigh pressure vessel 30 is firstly rotated by 180 degrees again (stepS8). As a result of the rotating operation, the first chamber 44 a islocated at the lower side. Therefore, the molten metal 14 in the secondchamber 44 b falls into the first chamber 44 a again.

The open pores of the porous sintered members 12 are infiltrated with apart of the molten metal 14 owing to the pressurization treatment(infiltration treatment) in step S7 described above. Therefore, themolten metal 14, which falls into the first chamber 44 a at the lowerside, is residual molten metal with which the porous sintered members 12are not infiltrated. When the residual molten metal falls into the firstchamber 44 a, the porous sintered members 12, which are infiltrated withthe molten metal 14, remain in the second chamber 44 b.

After that, the infiltrating gas in the high pressure vessel 30 isdischarged via the gas discharge tube 52. Simultaneously with thedischarging, the cooling gas is introduced into the high pressure vessel30 via the gas-introducing tube 50 (step S9). Owing to the discharge ofthe infiltrating gas and the introduction of the cooling gas, thecooling gas is thoroughly circulated in the high pressure vessel 30.Thus, the high pressure vessel 30 is quickly cooled. Owing to the quickcooling, the molten metal 14, with which the porous sintered member 12is infiltrated, is quickly solidified into mass of the metal 14, and thevolume is expanded. Therefore, the infiltrating metal 14 is tightlyretained in the porous sintered member 12.

Another cooling step is shown in a frame indicated by dashed lines inFIG. 3. The high pressure vessel 30 or the porous sintered member 12infiltrated with the molten metal 14 is transported to a cooling zonewhen the treatment in step S8 is completed. The high pressure vessel 30or the porous sintered member 12 infiltrated with the molten metal ismade contact with a chill block installed in the cooling zone (see stepS10).

By the contact with the chill block, the porous sintered member 12 isquickly cooled. The cooling process may be performed while blowing theporous sintered member 12 with a cooling gas, or cooling the chill blockwith water. Especially, it is preferable that the cooling is performedwhile taking the molten metal feeding effect into consideration.

The infiltration treatment for the porous sintered member 12 composed ofgraphite with the metal 14 can be easily carried out by performing therespective steps of the first production method as described above.Further, the infiltration ratio of the metal 14 in the porous sinteredmember 12 can be improved. It is possible to easily obtain the heat sinkmaterial 10A in which the average coefficient of thermal conductivity ofthose in the directions of the orthogonal three axes, or the coefficientof thermal conductivity in the direction of any axis is 180 to 220 W/mKor more, and the coefficient of thermal expansion is 1×10⁻⁶ to 10×10⁻⁶/°C.

However, when SiC is adopted for the porous sintered member as describedlater on, it is possible to obtain a heat sink material in which theaverage coefficient of thermal expansion of those from room temperatureto 200 ° C. is 4.0×10⁻⁶ to 9.0×10⁻⁶/° C., and the average coefficient ofthermal conductivity of those in the directions of the orthogonal threeaxes, or the coefficient of thermal conductivity in the direction of anyaxis is not less than 160 W/mK (room temperature), preferably not lessthan 180 W/mK.

In step S5 described above, when the heater 42 is powered to heat andmelt the metal 14 in the first chamber 44 a, it is desirable that thepredetermined temperature (heating temperature) to proceed to step S6 ispreferably a temperature higher than the melting point of the metal 14by 30° C. to 25° C., and more preferably a temperature higher than themelting point by 50° C. to 200° C. In this case, it is preferable thatthe interior of the high pressure vessel is in vacuum of not more than1×10⁻³ Torr.

In step S7 described above, the pressure applied to the high pressurevessel 30, by introducing the infiltrating gas into the high pressurevessel 30, is not less than 0.98 MPa and not more than 202 MPa. In thiscase, the pressure is preferably not less than 4.9 MPa and not more than202 MPa, and more preferably not less than 9.8 MPa and not more than 202MPa.

The higher pressure is preferred in view of the improvement ininfiltration ratio and the improvement in cooling ability. However, ifthe pressure is excessively high, then the graphite tends to bedestroyed, and the cost of the equipment endurable to the high pressureis expensive. Therefore, the pressure is selected in consideration ofthese factors.

It is preferable that the period of time to apply the pressure to thehigh pressure vessel 30 is favorably not less than 1 second and not morethan 60 seconds, and desirably not less than 1 second and not more than30 seconds.

As for the pores of the porous sintered member 12, as described above,it is desirable that those having an average diameter of 0.5 to 50 mmexist by not less than 90% by volume, and the porosity is 10 to 50% byvolume.

However, when SiC is adopted for a porous sintered member describedlater on, it is desirable that those having an average diameter of 5 to50 μm exist by not less than 90% by volume, and the porosity is 20 to70% by volume.

It is desirable that the cooling speed in the cooling step is preferably−400° C./hour or faster, and more preferably −800° C./hour or faster inthe period from the condition at temperature of the infiltration to thecondition at 800° C.

In step S7 described above, the pressure necessary to completelyinfiltrate the open pores of the porous sintered member 12 with themetal 14 is applied to the high pressure vessel 30. In this case, ifopen pores remain not infiltrated with the metal 14 in the poroussintered member 12, the thermal conductivity is extremely inhibited.Therefore, it is necessary to apply the high pressure.

The pressure can be roughly presumed in accordance with the Washburn'sequation. However, the smaller the pore diameter is, the larger thenecessary force is. According to this equation, a pressure of 39.2 MPais appropriate in the case of a pore meter having 0.1 μmφ, a pressure of3.92 MPa is appropriate in the case of 1.0 μmφ, and a pressure of 0.392MPa is appropriate in the case of 10 μmφ. However, pores of not morethan 0.01 μmφ actually exist in a material in which the average porediameter is 0.1 μmφ (see FIGS. 31 and 32). Therefore, it is necessary touse a larger pressure. Specifically a pressure of 392 MPa is required inthe case of 0.01 μmφ.

Preferred examples of the element to be added to the graphite and theelement to be added to the metal have been already described, andexplanation thereof is omitted in this section.

Next, explanation will be made with reference to FIGS. 4 and 5 forseveral modified methods of the first production method.

In the first modified method, as shown in FIG. 4, graphite is firstlysintered to prepare a porous sintered member 12 composed of graphite(step S101). For the initial state, the high pressure vessel 30 ispositioned at the lower side such that the first chamber 44 a of therefractory vessel 40 provided in the high pressure vessel 30 (stepS102).

After that, the porous sintered members 12 are set in the second chamber44 b, and the previously melted metal (molten metal) 14 is poured intothe first chamber 44 a (step S103).

Then, the high pressure vessel 30 is rotated by 180 degrees when themolten metal 14 in the first chamber 44 a arrives at a predeterminedtemperature (step S104). As a result of the rotating operation, themolten metal 14 in the first chamber 44 a falls into the second chamber44 b located at the lower side. Accordingly, the porous sintered member12 is infiltrated with the molten metal 14.

After that, the infiltrating gas is introduced into the high pressurevessel 30 via the gas-introducing tube 50 to pressurize the interior ofthe high pressure vessel 30 (step S105). By the pressurization, the openpores of the porous sintered members 12 are infiltrated with the moltenmetal 14.

Next, the second modified method will be explained with reference toFIG. 5. In an infiltrating step of the second modified embodiment, thehigh pressure vessel 30 is used, which includes a partition plate (notshown) composed of a porous ceramic material provided at a centralportion in the refractory vessel 40 installed in the high pressurevessel 30. The interior of the refractory vessel 40 is comparted by thepartition plate into a first chamber 44 a and a second chamber 44 b.

As for the partition plate, it is desirable to use a porous ceramicmaterial having the porosity of 40 to 90% by volume, and the porediameter of 0.5 to 3.0 mm. More preferably, it is desirable to use aporous ceramic material having the porosity is 70 to 85% by volume, andthe pore diameter of 1.0 to 2.0 mm.

In the second modified embodiment, as shown in FIG. 5, graphite isfirstly sintered to prepare a porous sintered member 12 of graphite(step S201). For the initial state, the high pressure vessel 30 islocated such that the first chamber 44 a of the refractory vessel 40provided in the high pressure vessel 30 is positioned on the lower side,and the second chamber 44 b is positioned on the upper side (step S202).

Then, the porous sintered members 12 and the ingot of the metal 14 areplaced in the refractory vessel 40 of the high pressure vessel 30. Theingot of the metal 14 is positioned on the upper side in the secondchamber 44 b, and the porous sintered members 12 are set in the firstchamber 44 a positioned on the lower side (step S203).

Subsequently, the high pressure vessel 30 (as well as refractory vessel40) is tightly enclosed, and then the evacuation is effected for theinterior of the high pressure vessel 30 by the aid of the suction tube48 so that the interior of the high pressure vessel 30 is in thenegative pressure state (step S204).

The heater 42 is powered to heat and melt the metal 14 in the secondchamber 44 b (step S205). When the molten metal 14 arrives at apredetermined temperature, the infiltrating gas is introduced into thehigh pressure vessel 30 via the gas-introducing tube 50 to pressurizethe interior of the high pressure vessel 30 (step S206). By thepressurization treatment, the molten metal 44 in the second chamber 44 bpositioned on the upper side passes through the partition plate, and theopen pores of the porous sintered members 12 in the first chamber 44 apositioned on the lower side are infiltrated therewith.

Next, a second production method will be explained with reference toFIGS. 6 to 8. In the second production method, a furnace 60 forsintering graphite to prepare the porous sintered member 12 as shown inFIG. 6 and a press machine 62 for infiltrating the porous sinteredmember 12 with the metal 14 as shown in FIG. 7 are used.

As shown in FIG. 6, the furnace 60 has inside thereof a space 72 capableof setting a case 70, and a heater 74 used to heat the case 70 set inthe space 72. The case 70 is composed of, for example, a material suchas graphite, ceramics, cerapaper (heat-insulating material composed ofceramics such as alumina). The graphite is set in the case 70.

As shown in FIG. 7, the press machine 62 has a mold 82 which has arecess 80 with an upper opening, and a punch 84 insertable into therecess 80 and forcibly pressing the contents in the recess 80downwardly.

Next, explanation will be made with reference to FIG. 8 for the secondproduction method based on the use of the furnace 60 and the pressmachine 62.

At first, the graphite is placed in the case 70, and the case 70 is setin the furnace 60 (step S301). The atmosphere in the furnace 60 isheated to sinter the graphite so that the porous sintered member 12 isprepared (step S302).

Alternatively, in this step, a current may be applied to the graphite toheat it up to about 3000° C. so that the porous sintered member 12 isprepared.

After that, the case 70 with the porous sintered member 12 therein istaken out of the furnace 60, and is set in the recess 80 of the pressmachine 62 (step S303).

Subsequently, the molten metal 86 of the metal 14 is poured into thecase 70 (step S304), and then the punch 84 is inserted into the recess80. The molten metal 86 in the case 70 is forcibly pressed downwardly(step S305). Owing to the pressing treatment with the punch 84, the openpores of the porous sintered member 12 are infiltrated with the moltenmetal 86 of the metal 14.

In the second production method described above, it is preferable thatthe pressure during the forcible pressing process with the punch 84 is1.01 to 202 MPa (10 to 2000 atmospheres). As shown in FIG. 7, gas ventholes 88, 90 and/or gaps for venting the gas remaining in the poroussintered member 12 may be formed at the bottom of the case 70 and/or thebottom of the mold 82. In this case, the gas remaining in the poroussintered member 12 is vented through 20 the gas vent holes 88, 90 duringthe forcible pressing process with the punch 84. Therefore, theinfiltration of the open pores with the molten metal 86 is smoothlyperformed.

As described above, when the respective steps of the second productionmethod are carried out, the porous sintered member 12 composed ofgraphite can be easily subjected to the infiltration treatment with themetal 14. Further, it is possible to improve the ratio of infiltrationof the porous sintered member 12 with the metal 14. It is possible toeasily obtain the heat sink material 10A in which the averagecoefficient of thermal conductivity of those in the directions of theorthogonal three axes, or the coefficient of thermal conductivity in thedirection of any axis is 180 to 220 W/mK or more, and the coefficient ofthermal expansion is 1×10⁻⁶ to 10×10⁻⁶/° C.

A furnace, which utilizes preheating, may be used in place of thefurnace 60 described above. In this case, a porous sintered member 12 ofa material previously formed into a compact or graphite is preheated.The graphite (or SiC as described later on) formed to have a network bythe aid of this treatment is easily infiltrated with the metal 14. Asfor the temperature for the preheating process, it is desirable that thepreheating is performed up to a temperature approximately equivalent tothe temperature of the molten metal 86. Specifically, when the moltenmetal 86 is at about 1200° C., it is desirable that the preheatingtemperature for the graphite is 1000 to 1400° C.

Next, a heat sink material 10B according to the second embodiment willbe explained with reference to FIG. 9.

As shown in FIG. 9, the heat sink material 10B according to the secondembodiment is constructed by mixing powder 12 a of carbon or allotropethereof and powder 14 a of metal 14, and forming an obtained mixture ata predetermined temperature under a predetermined pressure.

Those preferably used as the carbon or the allotrope thereof are thosehaving a coefficient of thermal conductivity of not less than 100 W/mK,desirably not less than 150 W/mK (estimated value when no pore exists),and more desirably not less than 200 W/mK (estimated value when no poreexists). Especially, in the second embodiment, it is possible to usediamond other than graphite. This embodiment is illustrative of the heatsink material 10B constructed by mixing powder of copper and powder ofgraphite having a coefficient of thermal conductivity of not less than100 W/mK, and forming an obtained mixture. It is possible to usealuminum and silver as the metal 14 other than copper.

The heat sink material 10B according to the second embodiment can bealso constructed by mixing a pulverized cut material of carbon orallotrope thereof (for example, a pulverized cut material of carbonfiber) and powder 14 a of the metal 14, and forming an obtained mixtureat a predetermined temperature under a predetermined pressure.

Considering the forming process to be performed in a press mold, it ispreferable that the predetermined temperature is relatively −10 to −50°C. with respect to a melting point of the metal 14. It is preferablethat the predetermined pressure is 10.13 to 101.32 MPa (100 to 1000atmospheres).

The average powder particle size of the powder 12 a of the carbon or theallotrope thereof and the powder 14 a of the metal 14 is preferably 1 μmto 500 μm. As for the volume ratios between the carbon or the allotropethereof and the metal 14, the volume ratio of the carbon or theallotrope thereof is within a range from 20 to 60% by volume, and thevolume ratio of the metal 14 is within a range from 80 to 40% by volume.Accordingly, it is possible to obtain the heat sink material 10B inwhich the average coefficient of thermal conductivity of those in thedirections of the orthogonal three axes, or the coefficient of thermalconductivity in the direction of any one axis is 200 to 350 W/mK ormore, and the coefficient of thermal expansion is 3×10⁻⁶ to 14×10⁻⁶/° C.

In the heat sink material 10B according to the second embodiment, it ispreferable that an additive, which makes it possible to performresintering after the forming process, is added to the carbon or theallotrope thereof. The additive may be exemplified by SiC and/or Si.Accordingly, the resintering can be performed at a temperature of notless than the melting point of the metal 14 after the forming process.In this case, grains generated after the forming process bind to oneanother as a result the resintering. Therefore, it is possible to almostexclude the grain boundary which inhibits the heat conduction. Thus, itis possible to improve the coefficient of thermal conductivity of theheat sink material 10B.

An element reacting with the carbon or the allotrope thereof may beadded into the carbon or the allotrope thereof. The additive elementincludes one or more of those selected from Ti, W, Mo, Nb, Cr, Zr, Be,Ta, V, B, and Mn. Accordingly, a reaction layer (carbide layer) isformed on the surface of the carbon or the allotrope thereof during theforming process and the resintering process. Thus, it is possible toimprove the binding of grains at the surface of the heat sink material10B.

It is preferable that a low melting point metal, for example, one ormore of those selected from Te, Bi, Pb, Sn, Se, Li, Sb, Tl, Ca, Cd, andNi are added to the metal 14. Accordingly, the wettability at theinterface between the carbon or the allotrope thereof and the metal 14is improved. It is possible to suppress the generation of the grainboundary which inhibits the heat conduction. In view of the heatconduction, it is preferable that the low melting point metal does notform solid solution with the metal 14.

It is also preferable that the metal 14 is added with one or more ofthose selected from Nb, Cr, Zr, Be, Ti, Ta, V, B, and Mn. Accordingly,it is possible to improve the reactivity of the carbon or the allotropethereof with the metal 14. Also in this case, it is possible to suppressthe occurrence of the grain boundary during the forming process.

It is preferable that an element, which has a temperature range ofsolid-liquid phase of not less than 30° C., desirably not less than 50°C., including, for example, one or more of those selected from Sn, P,Si, and Mg, is added to the metal 14 in order to improve molten metalflow performance and reduce the residual pores. Accordingly, it ispossible to reduce the dispersion during the infiltration, the residualpores are decreased, and it is possible to improve the strength. Theequivalent effect can be obtained also by increasing the infiltrationpressure.

It is preferable that an element to reduce the melting point is added tothe metal 14. The metal to be added is Zn, for example.

Next, explanation will be made with reference to FIGS. 10 to 14 forseveral methods (third and fourth production methods) to produce theheat sink material 10B according to the second embodiment.

At first, the third production method is carried out by using apreforming machine 100 (see FIG. 10) and a hot press machine 102 (seeFIG. 11). Those machines are shown by way of example only.

As shown in FIG. 10, the preforming machine 100 includes a mold 112which has a recess 110 with an upper opening, and a punch 114 insertableinto the recess 110 and forcibly pressing the contents in the recess 110downwardly. A mixture 104 obtained by mixing powder 12 a of carbon orallotrope thereof and powder 14 a of metal 14 is set in a case 70.

As shown in FIG. 11, the hot press machine 102 includes, in acylindrical casing 120, a lower punch 122 also serving as a basepedestal, a refractory vessel 124 made of graphite fixed on the lowerpunch 122 with an upper opening, an upper punch 126 movable back andforth from an upper position into the refractory vessel 124, and aheater 128 used to heat the refractory vessel 124. The refractory vessel124 receives a preformed product 106 of the mixture 104 formed by thepreforming machine 100 therein. The hot press machine 102 has a suctiontube 130 for evacuation.

A passage 132 is provided at the inside of the lower punch 122 in orderto flow a heating fluid for heating the interior of the refractoryvessel 124 and a cooling fluid for cooling the interior of therefractory vessel 124.

The third production method is carried out by in performing steps shownin FIG. 12. At first, the powder 12 a of carbon or allotrope thereof andthe powder 14 a of metal 14 are placed in the case 70 and are mixed witheach other to obtain a mixture 104 (step S401). Subsequently, the case70 containing the mixture 104 is set in the recess 110 of the mold 112of the preforming machine 100 (step S402). After that, the punch 114 isforcibly inserted into the recess 110, and the mixture 104 is preformedto form the preformed product 106 (step S403).

Subsequently, the preformed product 106 is taken out of the mold 112,and the preformed product 106 is set in the refractory vessel 124 of thehot press machine 102 (step S404). After tightly enclosing therefractory vessel 124, the interior of the refractory vessel 124 issubjected to evacuation by the aid of the suction tube 130 to give anegative pressure state in the refractory vessel 124 (step S405). Afterthat, the heater 128 is powered to make the temperature in therefractory vessel 124 be relatively −10 to −50° C. with respect to themelting point of the metal 14 (step S406).

When the temperature becomes a predetermined temperature, the upperpunch 126 is moved downwardly to pressurize the preformed product 106 sothat the heat sink material 10B is obtained (step S407). Then, theobtained product is used as the actual heat sink material 10B afterperforming a processing step etc. However, when the element enhancingthe binding force between the carbon or the allotrope thereof and themetal 14 is added, the heating may be performed over the melting pointof the metal 14 after the pressurization described above.

Preferred examples of the element to be added to the carbon or theallotrope thereof and the element to be added to the metal 14 have beenalready described, and detailed explanation thereof is omitted.

As described above, when the respective steps of the third productionmethod are carried out, it is possible to easily obtain the heat sinkmaterial 10B in which the average coefficient of thermal conductivity ofthose in the directions of the orthogonal three axes, or the coefficientof thermal conductivity in the direction of any axis is 200 to 350 W/mKor more, and the coefficient of thermal expansion is 3×10⁻⁶ to 14×10⁻⁶/°C.

Next, a fourth production method will be explained with reference toFIGS. 13 and 14. As shown in FIG. 14, the fourth production method iscarried out by using only the hot press machine 102 without using thepreforming machine 100.

As shown in FIG. 13, the powder 12 a of the carbon or the allotropethereof and the powder 14 a of the metal 14 are firstly placed in thecase 70, and are mixed with each other to obtain the mixture 104 (stepS501). The mixture 104 in the case 70 is directly set in the refractoryvessel 124 of the hot press machine 102 (step S502). After tightlyenclosing the refractory vessel 124, the interior of the refractoryvessel 124 is subjected to the evacuation by the aid of the suction tube130 to give a negative pressure state in the refractory vessel 124 (stepS503). After that, the heater 128 is powered to make the temperature inthe refractory vessel 124 be relatively −10 to −50° C. with respect tothe melting point of the metal 14 (step S504).

When the temperature becomes a predetermined temperature, the upperpunch 126 is moved downwardly to pressurize the mixture 104 so that theheat sink material 10B is obtained (step S505).

Also in the fourth production method, it is possible to easily obtainthe heat sink material 10B in which the average coefficient of thermalconductivity of those in the directions of the orthogonal three axes, orthe coefficient of thermal conductivity in the direction of any axis is200 to 350 W/mK or more, and the coefficient of thermal expansion is3×10⁻⁶ to 14×10⁻⁶/° C.

Next, a heat sink material 10C according to the third embodiment will beexplained with reference to FIG. 15.

As shown in FIG. 15, the heat sink material 10C according to the thirdembodiment is constructed by pressurizing a mixture obtained by mixingpowder 12 b of carbon or allotrope thereof and a binder (binding agent)etc. to prepare a preformed product or a block (preferably having acubic, rectangular parallelepiped, or arbitrary configuration), andinfiltrating the block with the metal. The same powder 12 b as thepowder 12 a of carbon or allotrope thereof used in the second embodimentmay be used. The heat sink material 10C can be manufactured to have anarbitrary shape which is approximate to the final shape.

Those usable as the carbon or the allotrope thereof other than graphiteinclude diamond. Those usable as the metal 14 other than copper includealuminum and silver.

The average powder particle size of the powder 12 b of the carbon or theallotrope thereof is 1 to 2000 μm. It is preferable that the lengthratio is not more than 1:5 between a direction in which the powder 12 bhas a minimum length and a direction in which the powder 12 b has amaximum length. In this case, although there is no strong network, it ispossible to make an arbitrary shape which is approximate to the finalshape. Therefore, it is also possible to omit the machining process tobe performed in downstream steps. As for the volume ratios between thepowder 12 b of the carbon or the allotrope thereof and the metal 14, itis desirable that the volume ratio of the carbon or the allotropethereof is within a range from 20 to 80% by volume, and the volume ratioof the metal 14 is within a range from 80 to 20% by volume.

It is desirable that an additive element to make reaction with thecarbon or the allotrope thereof is added into the powder 12 b of thecarbon or the allotrope thereof. The additive element may be selected inthe same manner as in the second embodiment.

It is desirable that respective additive elements are used for the metal14 in the same manner as in the first embodiment. The additive elementsmay include, for example, the additive element to improve thewettability, the additive element to improve the reactivity between thecarbon or the allotrope thereof and the metal 14, the additive elementto improve the molten metal flow performance, and the additive elementto lower the melting point.

Next, a fifth production method of the third embodiment will beexplained with reference to FIG. 16. In the fifth production method, atfirst, water and the binder (binding agent) are mixed with the powder 12b of the carbon or the allotrope thereof to prepare a mixture (stepS601).

The mixture is pressurized at a predetermined pressure to form apreformed product (step S602). The press machine 62 (see FIG. 7) or thepreforming machine 100 (see FIG. 10) may be used as a pressurizingapparatus.

Subsequently, the preheating treatment is performed in order that theobtained preformed product is easily infiltrated with the metal 14 (stepS603). As for the preheating temperature, for example, when the moltenmetal 14 is at about 1200° C., the preheating temperature for thegraphite is desirably 1000° C. to 1400° C. The binder used in step S601can be also removed by performing the preheating treatment.

Further, in step S604, the preformed product is sintered to form theblock. The sintering method is carried out in the same manner as in thefirst embodiment.

The preformed product is infiltrated with the molten metal 14 (stepS605). In the infiltrating step, the same treatments as those performedin the respective infiltrating steps described in the first embodimentmay be performed. For example, the heat sink material 10C can beobtained by executing the steps ranging from S2 to S9 in the firstproduction method (see FIG. 3) by using the high pressure vessel 30 (seeFIG. 2).

According to the fifth production method, the coefficient of thermalexpansion and the coefficient of thermal conductivity can be controlledto have desired values in the pressurization treatment performed in stepS602, depending on the condition of the pressed powder.

The obtained heat sink material 10C is characterized in that thecoefficient of thermal conductivity is more isotropic, and thewettability and the yield of material are also improved.

Further, the strength can be increased, because the metal 14 forms thenetwork. It is also possible to reduce the residual pores.

Further, it is possible to inexpensively produce the heat sink material10C. That is, the block before the infiltration cannot be machined,because it is fragile. However, the powder preformed product can besubjected to the infiltration after being formed to have a desiredshape. Further, the powder preformed product is endurable to someplastic deformation thereafter. Therefore, it is possible toinexpensively obtain the heat sink material 10C having a complicatedconfiguration.

Also in the fifth production method, the thermal expansion can bedecreased by adding the element to form carbide to the metal 14 in theinfiltration, in the same manner as in the respective production methodsdescribed above. Further, the infiltration ratio can be improved byadding the element to improve the wettability etc.

When a high infiltration pressure is applied, the infiltration ratio isincreased, and the strength and the coefficient of thermal conductivityare improved as well.

Examples of infiltration based on the fifth production method are nowshown in FIG. 17. Those indicated with “no pressurization” in the columnof the filling method shown in FIG. 17 shows a case where thepressurizing step, i.e., step S602 described above was omitted, and amixture obtained by spreading the powder was infiltrated with the metal14. Those indicated with “pressurization” show a case where 10 cm³ ofwater glass and 100 cm³ of water were added to 1000 cm³ of powder to becompacted, and was thereafter formed by removing the water and the waterglass during the preheating (1200° C.).

Next, explanation will be made with reference to FIG. 18 for a sixthproduction method for the heat sink material 10 a according to the thirdembodiment. In the sixth production method, at first, molten metal 14obtained by melting metal or metal in a solid-liquid coexisting state(solid-liquid co-existing metal) is prepared (step S701). In thisprocedure, the term “solid-liquid co-existing metal” refers to oneobtained by making metal (generally alloy) be in a semi-molten state orone obtained by cooling and agitating molten metal into a semisolidifiedstate. That is, the term refers to both of a metal in the semi-moltenstate obtained by heating and a metal in the semisolidified stateobtained by completely melting and being cooled afterwards.

Subsequently, the powder 12 a of carbon or allotrope thereof is mixedwith the molten metal 14 or the metal in the solid-liquid co-existingstate (step S702).

The molten metal 14 or the solid-liquid co-existing metal mixed with thepowder 12 a is cast into a desired shape. Accordingly, it is possible toobtain the heat sink material 10C (step S703).

The heat sink material 10C obtained by the sixth production method hasthe same feature as that of the heat sink material produced by the fifthproduction method.

Next, an exemplary experiment (first exemplary experiment) will bedescribed. In the first exemplary experiment, the type of the metal 14for infiltration, the type of the additive element, and the infiltratingmethod were changed for three respective types of carbons (P, M, and N)to observe the difference in coefficient of thermal conductivity betweentwo directions, the difference in coefficient of thermal expansionbetween two directions, the difference in bending strength between twodirections, the water resistance, and the effect of the additive elementrespectively. Results of this exemplary experiment are shown in FIGS. 19to 21. Respective characteristics of the three types of carbons (P, M,and N) are shown in FIG. 22.

The water resistance was inspected by placing a small amount of waterand a sample in a desiccator to give a state where the sample wasexposed to an atmosphere of water without being immersed in water.

At first, investigation is made for a case where a mold press was usedas the infiltrating method. The coefficient of thermal conductivity isgenerally higher in the samples infiltrated with copper alloy containingthe additive element than the samples infiltrated with pure copper. Thisresult contributes to the following reason. Basically, the coefficientof thermal conductivity is higher when pure copper is used. However,pure copper is inferior in wettability with respect to carbon, resultingin difficulty of infiltration. Further, the coefficient of thermalconductivity is lowered at the interface between the carbon and themetal after the infiltration.

When the sample is infiltrated with pure aluminum, a product having ahigh coefficient of thermal conductivity is obtained as compared withthe infiltration with pure copper, by the effect of generation ofcarbide and the high wettability with respect to the carbon. However,the coefficient of thermal conductivity is higher in the samplesinfiltrated with copper alloy containing additive element.

However, when the gas pressurization is used as the infiltrating method,the coefficient of thermal conductivity is higher than a case using themold press. The coefficient of thermal conductivity of the sampleinfiltrated with pure copper by the gas pressurization is approximatelythe same as that of the sample infiltrated with copper alloy containingadditive element. Representative examples are shown in FIG. 23, whichare extracted from the experimental results shown in FIGS. 19 to 21using the mold press and the gas pressurization.

The result described above is obtained, because the preheatingtemperature and the temperature of the molten metal are easilycontrolled when the gas pressurization is adapted. Of course, theinfiltration characteristic at the same level (high coefficient ofthermal conductivity) can be also obtained with the mold press by makingartifice on the equipment.

No specific difference was found in the coefficient of thermal expansionfor all of the carbons among those infiltrated with pure copper, thoseinfiltrated with copper alloy, and those infiltrated with pure aluminum.No specific difference was also found in the coefficient of thermalexpansion depending on the variety of the infiltrating method.

It is appreciated that those infiltrated with copper in alloy containingadditive element to improve the wettability have satisfactory waterresistance, and that those infiltrated with copper alloy containingadditive element to facilitate generation of carbide are improved inbending strength as compared with those constructed with only carbon.

In each of the samples, the ratio of coefficient of thermal conductivitybetween a surface direction (a certain direction parallel to the surfaceof the sample) and a thickness direction (a direction perpendicular tothe surface of the sample) is not more than 1:5, having a characteristicapproximately equal to the isotropic property. Therefore, when such asample is used as a heat sink, it is unnecessary to consider theinstallation direction case by case, which is advantageous in actualmounting.

Further, two exemplary experiments (second and third exemplaryexperiments) will be described. In these exemplary experiments, theinfiltration pressure in the vessel was changed upon the infiltration inthe infiltrating step for infiltrating carbon with metal in the firstembodiment in order to observe the residual pores, the density, theuniformity, the compressive strength, and the difference in coefficientsof thermal conductivity between the two orthogonal surface directionsrespectively.

The second exemplary experiment was carried out with infiltrationpressures of 26.7 MPa (272 kgf/cm²) and 156.0 MPa (1592 kgf/cm²).Results of the exemplary experiment are shown in FIG. 24.

In FIG. 24, the porosity (indicated by squares) and the density(indicated by circles) are plotted for the vertical axis, and theinfiltration pressure is plotted for the horizontal axis. The plot ofthe porosity is depicted by squares, and the plot of the density isdepicted by circles. According to the experimental results, it isunderstood that the density is increased and the porosity is decreasedwhen the high infiltration pressure is applied.

The compressive strength of carbon (standard: JIS R 1608, method fortesting compressive strength of fine ceramics) is 24.5 to 34.3 MPa (250to 350 kgf/cm²) in the surface direction and 34.3 to 44.1 MPa (350 to450 kgf/cm²) in the thickness direction. Therefore, according to thisexperiment, it has been confirmed that no problem arises in productioneven when the infiltration pressure having four to five times the carboncompressive strength is applied in the infiltrating step.

The third exemplary experiment was carried out with infiltrationpressures of 26.7 MPa (272 kgf/cm²) and 60.0 MPa (612 kgf/cm²). Resultsof this exemplary experiment are shown in FIGS. 25 to 29.

In FIG. 25, the measured density is plotted for the vertical axis, andthe average density of each lot is plotted for the horizontal axis.

According to FIG. 25, it is understood that the higher the infiltrationpressure is, the smaller the dispersion of the density average of eachlot is.

In FIGS. 26 to 28, the infiltration pressure is plotted for the verticalaxis, and the coefficient of thermal conductivity in the thicknessdirection, the compressive strength, and the density are plotted for thehorizontal axis. According to FIGS. 26 to 28, it is understood that thevalues of the respective characteristics are improved when the highinfiltration pressure is applied.

In FIG. 29, the difference in coefficients of thermal conductivitybetween the two orthogonal surface directions is plotted. One of thecoefficient of thermal conductivity is plotted for the horizontal axisas the X direction, and the other coefficient of thermal conductivity isplotted for the vertical axis as the Y direction. According to FIG. 29,it is understood that the dispersion in the surface direction is smallwhen the high infiltration pressure is applied.

It is considered that the respective effects are provided in the secondand third exemplary experiments described above, by the increase ininfiltration amount of the metal 14 by increasing the infiltrationpressure.

Further, two additional exemplary experiments (fourth and fifthexemplary experiments) will be described. In the fourth and fifthexemplary experiments, the infiltration pressure upon the infiltrationwith pressurization and the element to be added to the metal 14 werechanged to observe the change of the residual pores respectively in theinfiltrating step of infiltrating carbon with the metal 14 in the fourthembodiment.

The fourth exemplary experiment was carried out by adopting Cu0.1Nb forthe infiltration metal for cases of the original material withoutapplying the infiltration pressure and those pressurized at 27 MPa, 48MPa, and 60 MPa. Results of this exemplary experiment are shown in FIG.31.

In FIG. 31, the pore diameter is plotted for the horizontal axis, andthe residual pore volume is plotted for the vertical axis to observe thedifference among the cases of the respective infiltration pressures.According to FIG. 31, it is understood that the residual pore ratioafter the infiltration is decreased when the infiltration pressure isincreased.

The fifth exemplary experiment shows a case of no addition of element tothe metal for infiltration, a case of addition of Cu5Si, and a case ofaddition of Cu0.1Nb. The experiment was performed with infiltrationpressures of 27 MPa and 43 MPa. Results of this exemplary experiment areshown in FIG. 32.

The original material in FIG. 32 is under the same condition as that ofthe original material in FIG. 31. Therefore, their waveforms haveapproximately the same shape.

Cu5Si of the added element has a solid-liquid phase temperature range ofnot less than 30° C., and hence it has the good molten metal flowperformance (wettability) as compared with Cu0.1Nb. As a result, it isunderstood that the residual pores are decreased in the sample addedwith Cu5Si. A tendency is observed such that the residual pores afterthe infiltration are decreased when the infiltration pressure isincreased. This tendency is considered to be the same as the tendencyobserved in FIG. 31. It is possible to improve the strength bydecreasing the residual pores.

Next, explanation will be made for a case in which SiC is used as aporous sintered member in place of the carbon or the allotrope thereof.

When the additive to improve the wettability is introduced into SiC, itis preferable that the component of metal contains one or more additiveelements selected from Be, Al, Si, Mg, Ti, and Ni in a range up to 5%.Attention should be paid, because these elements are different fromthose of the case where carbon is utilized as the porous sinteredmember.

In order to improve the wettability between SiC and the metal 14, it ispreferable that Ni plating of 1 to 10% by volume, desirably 3 to 5% byvolume is previously applied to SiC. In this case, the infiltration at alow pressure can be realized. The Ni plating referred to herein shouldbe desirably a plating treatment with which no melting occurs duringpreheating such as plating of Ni—P—W or plating of Ni—B—W.

In order to improve the wettability between SiC and the metal 14, it ispreferable that SiC is previously infiltrated with Si by 1 to 10% byvolume, desirably 3 to 5% by volume. Also in this case, the infiltrationat a low pressure can be realized.

In relation to the procedure in which the Ni plating of 1 to 10% byvolume is previously applied to SiC, or SiC is previously infiltratedwith Si by 1 to 10% by volume, it is also preferable that palladiumplating is previously applied to SiC. In this case, combined plating ofNi and/or Si can be also applied, in addition to the palladium platingdescribed above.

The reaction may occur at a high temperature between SiC and the metal14, SiC may be decomposed into Si and C, and the original function maynot be exhibited. Therefore, it is necessary to shorten the period oftime in which SiC and the metal 14 make direct contact with each otherat a high temperature. The contact time between SiC and the metal 14 canbe shortened by satisfying a first treatment condition (pressure appliedto high pressure vessel 30=not less than 0.98 MPa (10 kgf/cm²) and notmore than 98 MPa (1000 kgf/cm²)), a second treatment condition (heatingtemperature=temperature higher by 30 to 250° C. than melting point ofmetal 14), or a third treatment condition plating of 1 to 10% by volumeis previously applied to SiC). Therefore, the decomposition reaction ofSiC as described above can be avoided beforehand.

It is necessary to apply a high pressure in order to sufficientlyinfiltrate SiC with the metal 14, because the wettability is poorbetween SiC and the metal 14. The pore surface of SiC is improved inquality to give good wettability between SiC and the metal 14 byeffecting the third treatment condition (Ni plating of 1 to 10% byvolume is previously applied to SiC) or a fourth treatment condition(SiC is previously infiltrated with Si by 1 to 10% by volume).Therefore, even finer pores can be also infiltrated with the metal 14 ata lower pressure.

Still another exemplary experiment (sixth exemplary experiment) will nowbe described. In the sixth exemplary experiment, the porosity of SiC,the pore diameter, the presence or absence of Ni plating, the presenceor absence of Si infiltration, the infiltration temperature, thepressurization pressure, the pressurization time, and the cooling speedwere changed to observe the difference of the reaction of SiC/Cu and theinfiltration of Cu under respective conditions. Obtained experimentalresults are shown in a table in FIG. 30. In FIG. 30, the reaction ofSiC/Cu was determined by the thickness (average value) of the reactionlayer formed between SiC and Cu. The determination condition is asfollows. The basis of the determination condition is the fact that whenthe reaction layer of not less than 5 μm is generated between SiC andCu, then the heat transfer between SiC and Cu is deteriorated, and thecoefficient of thermal conductivity is lowered in a composite materialfor a semiconductor heat sink. The following experimental results aresummarized:

-   -   (1)# if thickness (average) of reaction layer is not more than 1        μm→“no reaction”;    -   (2)# if thickness (average) of reaction layer is more than 1 μm        and not more than 5 μm→“slight reaction”; and    -   (3)# if thickness (average) of reaction layer is more than 5        μm→“strong reaction”.

According to the experimental results, the reaction of SiC/Cu is shownas “no reaction”, the infiltration situation of Cu is satisfactory, andthus good results are obtained in any of those which satisfypredetermined ranges for the porosity of SiC, the pore diameter, theinfiltration temperature, the pressurization pressure, thepressurization time, and the cooling speed respectively (samples 3, 7,8, 11, and 12).

As for samples 3, 7, 11, and 12 of the samples described above, the Niplating or the Si infiltration was performed. Therefore, the wettabilitywith Cu is satisfactory. The good results as described above wereobtained even when the pressurization time was shortened. As for sample8, the Ni plating and the Si infiltration were not performed. However,the pressurization time could be successfully shortened by increasingthe pressurization pressure. Thus, the good results as described abovewere obtained.

The infiltration situation of Cu is insufficient for any of samples 1,5, and 9 in which the pressurization pressure was 0.78 MPa (8 kgf/cm²)which was lower than the predetermined range described above. Amongthese samples, the reaction situation of SiC/Cu is shown as “strongreaction” for those in which the pressurization time is long (samples 1and 5).

As for sample 6, the infiltration situation is insufficient, althoughthe reaction situation of SiC/Cu is shown as “slight reaction.” Thisseems to be because the porosity and the pore diameter do not satisfythe predetermined ranges respectively. As for sample 14, the reaction ofSiC/Cu is shown as “strong reaction”, although the infiltrationsituation is satisfactory. This seems to be because the pore diameter islarger than the predetermined range, and the pressurization time isrelatively long.

Next, explanation will be made for embodiments based on the use of SiCfor the porous sintered member. At first, the steps of sinteringgraphite to prepare the porous sintered member (step S1, step S101, stepS201, step S301, and step S302) are unnecessary when SiC is utilized inthe first embodiment described above (first production method, firstmodified method, second modified method, and second production method).The subsequent steps will be the same for producing the heat sinkmaterial.

Explanation will be made with reference to FIGS. 33 to 36 for aproduction method (seventh production method) according to the fourthembodiment as an embodiment based on the use of SiC for the poroussintered member.

The seventh production method is carried out by using a hot pressmachine 1060 as specifically shown in FIG. 33 by way of example. The hotpress machine 1060 has approximately the same structure as that of thehot press machine 102 explained in the second embodiment. However, forconvenience, the seventh production method will be described with theseparate drawing.

The hot press machine 1060 has, in a cylindrical casing 1062, a lowerpunch 1064 also serving as a base pedestal, a refractory vessel 1066fixed on the lower punch 1064 with an upper opening, an upper punch 1068movable back and forth from an upper position into the refractory vessel1066, and a heater 1070 used to heat the refractory vessel 1066. The hotpress machine 1060 is provided with a suction tube 1072 for evacuation.

The refractory vessel 1066 has a cylindrical configuration with a hollowsection 1074. A flange 1076 is provided on the side surface of the upperpunch 1068 for determining the throw (stroke) of the upper punch 1068. Apacking 1078 is attached to the lower surface of the flange 1076. Thepacking 1078 makes contact with the upper circumferential surface of therefractory vessel 1066 in order to give a tightly enclosed state of therefractory vessel 1066. A passage 1080 is provided at the inside of thelower punch 1064. The passage 1080 is used to flow the heating fluid forheating the interior of the refractory vessel 1066 and the cooling fluidfor cooling the interior of the refractory vessel 1066.

The seventh production method is carried out by performing steps shownin FIG. 34.

At first, SiC 1020, a filter 1054 made of porous ceramics, and ingots ofmetal 14 are introduced in this order from the bottom of the hollowsection 1074 of the refractory vessel 1066 (step S1301). For the filter1054, it is desirable to use a porous ceramic material having a porosityof 40 to 90% and a pore diameter of 0.5 to 3.0 mm. It is more preferableto use a porous ceramic material having a porosity of 70 to 85% and apore diameter of 1.0 to 2.0 mm.

The filter 1054 functions as a partition plate separating the SiC 1020and the ingots of metal 14 so that they are placed in a non-contactstate. An upper chamber 1074 a is defined in the hollow section 1074 forsetting the ingots of metal 14 on the filter 1054. A lower chamber 1074b is defined for setting the SiC 1020 under the filter 1054.

Subsequently, the refractory vessel 1066 is tightly enclosed, and thenthe evacuation is effected for the interior of the refractory vessel1066 by the aid of the suction tube 1072 so that the both chambers 1074a, 1074 b of the refractory vessel 1066 are in a negative pressure state(step S1302).

After that, the heater 1070 is powered to heat and melt the metal 14 inthe upper chamber 1074 a (step S1303). During this process, a heatingfluid may be made flow through a passage 1080 of the lower punch 1064 incombination with the electric power application to the heater 1070 sothat the interior of the refractory vessel 1066 may be heated.

The upper punch 1068 is moved downwardly when the melted matter of themetal 14 (molten metal) in the upper chamber 1074 a arrives at apredetermined temperature to pressurize the interior of the upperchamber 1074 a up to a predetermined pressure (step S1304). During thisprocess, the refractory vessel 1066 is tightly enclosed by the mutualpressurization and the contact between the upper circumferential surfaceof the refractory vessel 1066 and the packing 1078 attached to theflange 1076 of the upper punch 1068. It is possible to effectively avoidsuch an inconvenience that the molten metal inside may leak to theoutside of the refractory vessel 1066.

The melted matter of the metal 14 (molten metal) at the predeterminedpressure in the upper chamber 1074 a is extruded by the pressure in theupper chamber 1074 a through the filter 1054 toward the lower chamber1074 b, and introduced into the lower chamber 1074 b. At the same time,The SiC 1020 in the lower chamber 1074 b is infiltrated with the moltenmetal.

When the time comes to the end point previously set in accordance withthe time management (point of time when the infiltration of the SiC 1020with the molten metal 14 is in a saturated state), a cooling fluid inturn flows through the passage 1080 in the lower punch 1064 so that therefractory vessel 1066 is cooled in a direction from the bottom towardthe top (step S1305). Accordingly, the molten metal 14, with which theSiC 1020 is infiltrated, is solidified. The pressurized state in therefractory vessel 1066 effected by the upper punch 1068 and the lowerpunch 1064 is retained until the solidification is completed.

When the solidification is completed, SiC 1020 infiltrated with themetal 14 is taken out of the refractory vessel 1066 (step 1306).

In this production method, the SiC 1020 and the metal 14 are heatedwhile being sufficiently degassed. After the metal 14 is melted, themetal 14 is immediately made contact with the SiC 1020. Further, themetal 14 and the SiC 1020 are in the pressurized state, and thepressurized state is maintained until when the cooling operation iscompleted.

Therefore, the SiC 1020 can be efficiently infiltrated with the metal14. In the embodiment described above, the infiltration treatment isperformed at the negative pressure. However, the infiltration treatmentmay be performed at the atmospheric pressure.

As described above, both of the molten metal 14 and the SiC 1020 makecontact with each other after being pressurized so that the infiltrationtreatment is performed. Therefore, it is possible to minimize thedecrease in pressure caused when both make contact with each other.Thus, it is possible to maintain the satisfactory pressurization stateduring the infiltration treatment.

In the embodiment described above, the packing 1078 is provided at thelower surface of the flange 1076 of the upper punch 1068 in order toavoid the leakage of the molten metal 14. However, as indicated bytwo-dot chain lines in FIG. 33, a packing 1078 may be provided at theupper circumferential surface of the refractory vessel 1066.Alternatively, a packing member 1102 may be provided at a lower portionof the upper punch 1068 as shown in FIG. 36. The packing member 1102 hastwo ring-shaped divided type packings 1100 superimposed as shown in FIG.35A. In this case, the molten metal enters a hollow section 1104 of thepacking member 1102, and thus the diameter of each of the divided typepackings 1100 is enlarged. As a result, the upper chamber 1074 a istightly enclosed, and the leakage of the molten metal 14 is avoided.

Next, a modified method of the seventh production method will beexplained with reference to FIGS. 37 and 38. Constitutive componentscorresponding to those shown in FIG. 33 are designated by the samereference numerals, and duplicate explanation thereof will be omitted.

The production method according to this modified method uses a hot pressmachine 1060 as shown in FIG. 37. In the hot press machine 1060, afilter member 1110 of porous ceramics is secured to a central portion inthe height direction of a hollow section 1074 of a refractory vessel1066, and a door 1112 is attached openably/closably to a side surface ofa lower chamber 1074 b. A portion of the hollow section 1074 of therefractory vessel 1066 disposed over the filter member 1110 serves as anupper chamber 1074 a, and a portion disposed under the filter member1110 serves as a lower chamber 1074 b. Especially, the door 1112attached to the lower chamber 1074 b makes the lower chamber 1074 btightly enclosed when the door 1112 is closed.

The modified production method is carried out by performing steps shownin FIG. 38.

At first, ingots of metal 14 are introduced into the upper chamber 1074a of the refractory vessel 1066, and the door 1112 of the lower chamber1074 b is opened to introduce SiC 1020 into the lower chamber 1074 b(step S1401).

Subsequently, the door 1112 is closed to tightly enclose the lowerchamber 1074 b. Further, the hot press machine 1060 is tightly enclosed.After that, the evacuation is effected for the interior of therefractory vessel 1066 by the aid of the suction tube 1072 so that theboth chambers 1074 a, 1074 b of the refractory vessel 1066 are in anegative pressure state (step S1402).

After that, the heater 1070 is powered to heat and melt the metal 14 inthe upper chamber 1074 a (step S1403). Also in this case, a heatingfluid may be made flow through the passage 1080 of the lower punch 1064in combination with the electric power application to the heater 1070 sothat the interior of the refractory vessel 1066 can be heated.

When the melted matter of the metal 14 (molten metal) in the upperchamber 1074 a comes to a predetermined temperature, the upper punch1068 is moved downwardly to pressurize the interior of the upper chamber1074 a up to a predetermined pressure (step S1404).

The melted matter of the metal 14 (molten metal) in the upper chamber1074 a having arrived at the predetermined pressure is extruded by thepressure in the upper chamber 1074 a through the filter member 1110toward the lower chamber 1074 b, and it is introduced into the lowerchamber 1074 b. At the same time, the SiC 1020 installed in the lowerchamber 1074 b is infiltrated with the molten metal.

When the time comes to the end point previously set in accordance withthe time management, a cooling fluid is in turn made flow through thepassage 1080 in the lower punch 1064 so that the refractory vessel 1066is cooled in a direction from the bottom toward the top (step S1405).Accordingly, the molten metal 14, with which the SiC 1020 isinfiltrated, is solidified.

When the solidification is completed, the SiC 1020 infiltrated with themetal 14 is taken out of the refractory vessel 1066 (step 1406).

Also in this modified production method, the SiC 1020 can be efficientlyinfiltrated with the metal 14 in the same manner as in the seventhproduction method. Also in this modified method, both of the moltenmetal 14 and the SiC 1020 make contact with each other after beingpressurized so that the infiltration treatment is performed. Therefore,it is possible to minimize the decrease in pressure caused when bothmake contact with each other. Thus, it is possible to maintain thesatisfactory pressurization state during the infiltration treatment. Inthis modified method, the infiltration treatment is performed at thenegative pressure. However, the infiltration treatment may be performedat the atmospheric pressure.

Further, explanation will be made with reference to FIGS. 39 and 40 fora production method (eighth production method) according to the fifthembodiment as an embodiment in which SiC is utilized for the poroussintered member. Constitutive components corresponding to those shown inFIG. 33 are designated by the same reference numerals, duplicateexplanation of which will be omitted.

The eighth production method is in principle approximately the same asthe production method according to the fourth embodiment describedabove. However, the former is different from the latter in that SiC 1020and the metal 14 make contact with each other at a negative pressure orat the atmospheric pressure in the infiltrating step, and a heatingtreatment is performed to melt the metal 14.

Specifically, the eighth production method differs in that the filter1054 is not introduced into the refractory vessel 1066 of the hot pressmachine 1060 used in the production method according to the thirdembodiment shown in FIG. 33, and the SiC 1020 and the metal 14 areintroduced in this order from the bottom of the vessel 1060.

The production method according to the fifth embodiment is carried outby performing steps shown in FIG. 40.

At first, the SiC 1020 and ingots of the metal 14 are introduced in thisorder from the bottom of the hollow section 1074 of the refractoryvessel 1066 (step S1501).

Subsequently, the hot press machine 1060 is tightly enclosed, and thenthe interior of the refractory vessel 1066 is subjected to theevacuation by the aid of the suction tube 1072 so that the interior ofthe refractory vessel 1066 is in a negative pressure state (step S1502).

After that, the heater 1070 is powered to heat and melt the metal 14 inthe refractory vessel 1066 (step S1503). During this process, a heatingfluid may be made flow through the passage 1080 of the lower punch 1064in combination with the electric power application to the heater 1070 sothat the interior of the refractory vessel 1066 may be heated.

When the melted matter of the metal 14 (molten metal) in the refractoryvessel 1066 arrives at a predetermined temperature, the upper punch 1068is moved downwardly to pressurize the interior of the refractory vessel1066 up to a predetermined pressure (step S1504).

The SiC 1020 is infiltrated with the melted matter of the metal 14(molten metal) having arrived at the predetermined pressure inaccordance with the pressure in the refractory vessel 1066.

When the time comes to the end point previously set in accordance withthe time management (point of time at which the infiltration of the SiC1020 with the molten metal is in a saturated state), a cooling fluid isin turn made flow through the passage 1080 in the lower punch 1064 sothat the refractory vessel 1066 is cooled in a direction from the bottomtoward the top (step S1505). Accordingly, the molten metal, with whichthe SiC 1020 is infiltrated, is solidified. The pressurized state in therefractory vessel 1066 effected by the upper punch 1068 and the lowerpunch 1064 is retained until the solidification is completed.

When the solidification is completed, the SiC 1020 infiltrated with themetal 14 is taken out of the refractory vessel 1066 (step 1506).

Also in this eighth production method, the SiC 1020 and the metal 14 areheated while being sufficiently degassed. After the metal 14 is meltedin the state where the metal 14 and the SiC 1020 make contact with eachother, the interior of the refractory vessel 1066 is in the pressurizedstate. Further, the pressurization is maintained until the point of timewhen the cooling operation is completed. Therefore, the SiC 1020 can beefficiently infiltrated with the metal 14.

It is a matter of course that the heat sink material and the method ofproducing the same according to the present invention are not limited tothe embodiments and methods described above, which may be embodied inother various forms without deviating from the gist or essentialcharacteristics of the present invention.

1. A heat sink material comprising carbon or graphite and metal which isat least one selected from Cu, Al, and Ag, said metal having one or moreof Te, Bi, Pb, Sn, Se, Li, Sb, Tl, Ca and Cd added thereto for improvingwettability at an interface between said carbon or graphite and saidmetal, wherein said heat sink material is constructed by infiltrating aporous sintered member with said metal, said porous sintered memberbeing obtained by sintering said carbon or said graphite to form anetwork, wherein an average coefficient of thermal conductivity of thosein directions of orthogonal three axes, or a coefficient of thermalconductivity in a direction of any axis is not less than 180 W/mK, and aratio of coefficient of thermal conductivity is not more than 1:5between a direction in which said coefficient of thermal conductivity isminimum and a direction in which said coefficient of thermalconductivity is maximum, and wherein a coefficient of thermal expansionis 1×10⁻⁶ to 10×10⁻⁶/° C.
 2. The heat sink material according to claim1, wherein an additive is added to said carbon or said graphite fordecreasing a closed porosity when said carbon or said graphite issintered.
 3. The heat sink material according to claim 2, wherein saidadditive for decreasing said closed porosity is at least one selectedfrom SiC and Si.
 4. The heat sink material according to claim 1, whereina closed porosity is not more than 12% by volume.
 5. The heat sinkmaterial according to claim 1, wherein said carbon or said graphite hasa coefficient of thermal conductivity of not less than 100 W/mK.
 6. Theheat sink material according to claim 1, wherein as for volume ratiosbetween said carbon or said graphite and said metal, said volume ratioof said carbon or said graphite is within a range from 20 to 80% byvolume, and said volume ratio of said metal is within a range from 80 to20% by volume.
 7. A heat sink material comprising carbon or graphite andmetal which is at least one selected from Cu, Al, and Ag, said metalhaving one or more of Nb, Cr, Zr, Be, Ti, Ta, V, B and Mn added toimprove reactivity with said carbon or graphite, wherein said heat sinkmaterial is constructed by infiltrating a porous sintered member withsaid metal, said porous sintered member being obtained by sintering saidcarbon or said graphite to form a network, wherein an averagecoefficient of thermal conductivity of those in directions of orthogonalthree axes, or a coefficient of thermal conductivity in a direction ofany axis is not less than 180 W/mK, and a ratio of coefficient ofthermal conductivity is not more than 1:5 between a direction in whichsaid coefficient of thermal conductivity is minimum and a direction inwhich said coefficient of thermal conductivity is maximum, and wherein acoefficient of thermal expansion is 1×10⁻⁶ to 10×10⁻⁶/° C.
 8. The heatsink material according to claim 7, wherein an additive is added to saidcarbon or said graphite for decreasing a closed porosity when saidcarbon or said graphite is sintered.
 9. The heat sink material accordingto claim 8, wherein said additive for decreasing said closed porosity isat least one selected from SiC and Si.
 10. The heat sink materialaccording to claim 7, wherein a closed porosity is not more than 12% byvolume.
 11. The heat sink material according to claim 7, wherein saidcarbon or said graphite has a coefficient of thermal conductivity of notless than 100 W/mk.
 12. The heat sink material according to claim 7,wherein as for volume ratios between said carbon or said graphite andsaid metal, said volume ratio of said carbon or said graphite is withina range from 20 to 80% by volume, and said volume ratio of said metal iswithin a range from 80 to 20% by volume.
 13. A heat sink materialcomprising carbon or graphite and metal which is at least one selectedfrom Cu and Ag, said metal includes an element added thereto to improvemolten metal flow performance, said element added to said metal has atemperature range of solid phase/liquid phase of not less than 30° C.,wherein said heat sink material is constructed by infiltrating a poroussintered member with said metal, said porous sintered member beingobtained by sintering said carbon or said graphite to form a network,wherein an average coefficient of thermal conductivity of those indirections of orthogonal three axes, or a coefficient of thermalconductivity in a direction of any axis is not less than 180 W/mK, and aratio of coefficient of thermal conductivity is not more than 1:5between a direction in which said coefficient of thermal conductivity isminimum and a direction in which said coefficient of thermalconductivity is maximum, and wherein a coefficient of thermal expansionis 1×10⁻⁶to 10×10⁻⁶/° C.
 14. The heat sink material according to claim13, wherein said element added to said metal comprises Si.
 15. The heatsink material according to claim 13, wherein an additive is added tosaid carbon or said graphite for decreasing a closed porosity when saidcarbon or said graphite is sintered.
 16. The heat sink materialaccording to claim 15, wherein said additive for decreasing said closedporosity is at least one selected from SiC and Si.
 17. The heat sinkmaterial according to claim 13, wherein a closed porosity is not morethan 12% by volume.
 18. The heat sink material according to claim 13,wherein said carbon or said graphite has a coefficient of thermalconductivity of not less than 100 W/mK.
 19. The heat sink materialaccording to claim 13, wherein as for volume ratios between said carbonor said graphite and said metal, said volume ratio of said carbon orsaid graphite is within a range from 20 to 80% by volume, and saidvolume ratio of said metal is within a range from 80 to 20% by volume.20. A heat sink material comprising carbon or graphite and metal whichis at least one selected from Cu, Al, and Ag, said metal having anelement added thereto for lowering a melting point of said metal,wherein said heat sink material is constructed by infiltrating a poroussintered member with said metal, said porous sintered member beingobtained by sintering said carbon or said graphite to form a network,wherein an average coefficient of thermal conductivity of those indirections of orthogonal three axes, or a coefficient of thermalconductivity in a direction of any axis is not less than 180 W/mK, and aratio of coefficient of thermal conductivity is not more than 1:5between a direction in which said coefficient of thermal conductivity isminimum and a direction in which said coefficient of thermalconductivity is maximum, and wherein a coefficient of thermal expansionis 1×10⁻⁶ to 10×10⁻⁶/° C.
 21. The heat sink material according to claim20, wherein said element to be added is Zn.
 22. The heat sink materialaccording to claim 20, wherein an additive is added to said carbon orsaid graphite for decreasing a closed porosity when said carbon or saidgraphite is sintered.
 23. The heat sink material according to claim 22,wherein said additive for decreasing said closed porosity is at leastone selected from SiC and Si.
 24. The heat sink material according toclaim 20, wherein a closed porosity is not more than 12% by volume. 25.The heat sink material according to claim 20, wherein said carbon orsaid graphite has a coefficient of thermal conductivity of not less than100 W/mK.
 26. The heat sink material according to claim 20, wherein asfor volume ratios between said carbon or said graphite and said metal,said volume ratio of said carbon or said graphite is within a range from20 to 80% by volume, and said volume ratio of said metal is within arange from 80 to 20% by volume.
 27. A heat sink material comprisingcarbon or graphite and metal which is at least one selected from Cu, Al,and Ag, said metal having an element added thereto for improving acoefficient of thermal conductivity of said heat sink material, whereinsaid heat sink material is constructed by infiltrating a porous sinteredmember with said metal, said porous sintered member being obtained bysintering said carbon or said graphite to form a network, wherein saidadded element being alloyed with said met to obtain an alloy which isdeposited on the surface of said metal after heat treatment and reactionwith carbon, and wherein said alloy has an initial coefficient ofthermal conductivity of not less than 10 W/mk. wherein an averagecoefficient of thermal conductivity of said heat sink material indirections of orthogonal three axes, or a coefficient of thermalconductivity in a direction of any axis is not less than 180 W/mK, and aratio of coefficient of thermal conductivity is not more than 1:5between a direction in which said coefficient of thermal conductivity isminimum and a direction in which said coefficient of thermalconductivity is maximum, and wherein a coefficient of thermal expansionis 1×10⁻⁶ to 10×10⁻⁶/° C.
 28. The heat sink material according to claim27, wherein an additive is added to said carbon or said graphite fordecreasing a closed porosity when said carbon or said graphite issintered.
 29. The heat sink material according to claim 28, wherein saidadditive for decreasing said closed porosity is at least one selectedfrom SiC and Si.
 30. The heat sink material according to claim 27,wherein a closed porosity is not more than 12% by volume.
 31. The heatsink material according to claim 27, wherein said carbon or saidgraphite has a coefficient of thermal conductivity of not less than 100W/mK.
 32. The heat sink material according to claim 27, wherein as forvolume ratios between said carbon or said graphite and said metal, saidvolume ratio of said carbon or said graphite is within a range from 20to 80% by volume, and said volume ratio of said metal is within a rangefrom 80 to 20% by volume.
 33. A heat sink material comprising carbon orgraphite and metal which is at least one selected from Cu, Al, and Ag,wherein a carbide layer is formed on a surface of said carbon or saidgraphite, wherein an average coefficient of thermal conductivity ofthose in directions of orthogonal three axes, or a coefficient ofthermal conductivity in a direction of any axis is not less than 180W/mK, and a ratio of coefficient of thermal conductivity is not morethan 1:5 between a direction in which said coefficient of thermalconductivity is minimum and a direction in which said coefficient ofthermal conductivity is maximum, and wherein a coefficient of thermalexpansion is 1×10⁻⁶ to 10×10⁻⁶/° C.
 34. The heat sink material accordingto claim 33, wherein an element for forming a carbide layer is added tosaid metal, and wherein said carbide layer is formed on the basis of areaction at least between said carbon or said graphite and the elementto be added.
 35. The heat sink material according to claim 34, whereinsaid element to be added is one or more of those selected from Ti, W,Mo, Nb, Cr, Zr, Be, Ta, V, B, and Mn.
 36. A heat sink materialcomprising carbon or graphite and metal which is at least one selectedfrom Cu, Al, and Ag, wherein said heat sink material is constructed byinfiltrating a porous sintered member with said metal, said poroussintered member being obtained by sintering said carbon or said graphiteto form a network, wherein an element which has a temperature range ofsolid phase/liquid phase of not less than 30° C. is added to said metalin order to improve molten metal flow performance, wherein an averagecoefficient of thermal conductivity of those in directions of orthogonalthree axes, or a coefficient of thermal conductivity in a direction ofany axis is not less than 180 W/mK, and a ratio of coefficient ofthermal conductivity is not more than 1:5 between a direction in whichsaid coefficient of thermal conductivity is minimum and a direction inwhich said coefficient of thermal conductivity is maximum, and wherein acoefficient of thermal expansion is 1×10⁻⁶ to 10×10⁻⁶/° C.
 37. The heatsink material according to claim 36, wherein said element to be added isone or more of those selected from Sn, P and Mg.
 38. The heat sinkmaterial according to claim 37, wherein said element to be added is Si.